Date Utilities

The headless package exports a set of native Date helper functions. These replace the need for libraries like dayjs or date-fns — the library has zero external date dependencies.

All functions are pure (they return new Date objects rather than mutating the input).

Import

import {
  today,
  parseDate,
  startOf,
  endOf,
  add,
  subtract,
  isSame,
  isBefore,
  isAfter,
  diff,
  daysInMonth,
  setYear,
  setMonth,
  setDate,
  setHour,
  setMinute,
  setSecond,
  formatBasic,
} from "react-date-range-picker-headless";

DateUnit Type

Most functions accept a DateUnit parameter:

type DateUnit = "year" | "month" | "week" | "day" | "hour" | "minute" | "second" | "millisecond";

Functions

today

Returns the current date/time.

const now = today(); // new Date()

parseDate

Parse a value into a Date object. Returns new Date() if the input is falsy.

parseDate("2026-03-01"); // Date
parseDate(1709251200000); // Date from timestamp
parseDate(existingDate); // Clone
parseDate(null); // new Date() (fallback)

Signature: parseDate(date?: Date | string | number | null): Date

startOf

Get the start of a unit of time.

startOf(date, "day"); // 2026-03-01 00:00:00.000
startOf(date, "month"); // 2026-03-01 00:00:00.000
startOf(date, "year"); // 2026-01-01 00:00:00.000
startOf(date, "week"); // Start of week (default Sunday)
startOf(date, "week", 1); // Start of week (Monday)

Signature: startOf(date: Date, unit: DateUnit, weekStartsOn?: number): Date

endOf

Get the end of a unit of time.

endOf(date, "day"); // 2026-03-01 23:59:59.999
endOf(date, "month"); // 2026-03-31 23:59:59.999
endOf(date, "year"); // 2026-12-31 23:59:59.999

Signature: endOf(date: Date, unit: DateUnit, weekStartsOn?: number): Date

add

Add an amount of time to a date.

add(date, 1, "day"); // Tomorrow
add(date, 3, "month"); // 3 months later
add(date, -1, "year"); // 1 year ago
add(date, 2, "hour"); // 2 hours later

Handles month overflow (e.g. Jan 31 + 1 month = Feb 28, not Mar 3).

Signature: add(date: Date, amount: number, unit: DateUnit): Date

subtract

Subtract an amount of time from a date. Equivalent to add(date, -amount, unit).

subtract(date, 7, "day"); // 7 days ago
subtract(date, 1, "month"); // 1 month ago

Signature: subtract(date: Date, amount: number, unit: DateUnit): Date

isSame

Check if two dates are the same at a given unit of precision.

isSame(date1, date2, "day"); // Same calendar day?
isSame(date1, date2, "month"); // Same month?
isSame(date1, date2, "year"); // Same year?
isSame(null, date2, "day"); // false (null-safe)

Signature: isSame(date1: Date | null | undefined, date2: Date | null | undefined, unit?: DateUnit): boolean

isBefore

Check if the first date is before the second at a given precision.

isBefore(date1, date2, "day"); // Is date1 on an earlier day?
isBefore(date1, date2); // Millisecond comparison

Signature: isBefore(date1: Date, date2: Date, unit?: DateUnit): boolean

isAfter

Check if the first date is after the second at a given precision.

isAfter(date1, date2, "day"); // Is date1 on a later day?

Signature: isAfter(date1: Date, date2: Date, unit?: DateUnit): boolean

diff

Get the difference between two dates in a given unit.

diff(date1, date2, "day"); // Number of days between
diff(date1, date2, "month"); // Number of months between
diff(date1, date2, "year"); // Number of years between

Signature: diff(date1: Date, date2: Date, unit: DateUnit): number

daysInMonth

Get the number of days in a date’s month.

daysInMonth(new Date(2026, 1)); // 28 (February 2026)
daysInMonth(new Date(2026, 0)); // 31 (January 2026)

Signature: daysInMonth(date: Date): number

setYear / setMonth / setDate / setHour / setMinute / setSecond

Set a specific part of a date, returning a new Date.

setYear(date, 2027); // Change year to 2027
setMonth(date, 5); // Change to June (0-indexed)
setDate(date, 15); // Change to 15th
setHour(date, 14); // Change to 2 PM
setMinute(date, 30); // Change to :30
setSecond(date, 0); // Change to :00

setYear and setMonth handle overflow (e.g. Feb 29 in a leap year, set to a non-leap year, clamps to Feb 28).

Signatures:

• setYear(date: Date, year: number): Date
• setMonth(date: Date, month: number): Date
• setDate(date: Date, day: number): Date
• setHour(date: Date, hour: number): Date
• setMinute(date: Date, minute: number): Date
• setSecond(date: Date, second: number): Date

formatBasic

Format a date using a template string.

formatBasic(date, "YYYY-MM-DD"); // "2026-03-01"
formatBasic(date, "YYYY/MM/DD HH:mm:ss"); // "2026/03/01 14:30:00"
formatBasic(date, "M/D"); // "3/1"
formatBasic(date, "hh:mm A"); // Note: A token not supported, use period from hook

Supported tokens:

Signature: formatBasic(date: Date, format: string): string